The present invention relates to semiconductor die packaging and, more particularly, to a semiconductor package and a lead frame for a semiconductor package.
When a semiconductor die is packaged with a lead-frame, the semiconductor die is mounted to a die attach pad, often called a flag. Tie bars attach the flag to an outer frame of the lead frame. The lead frame has lead fingers extending from the outer frame towards the flag. The lead fingers have external connector pads, that are wire bonded to pads or electrodes of the die, and provide a means of easily electrically connecting the die to circuit boards and the like. After the electrodes and external connector pads are electrically connected, the semiconductor die and a part of the lead fingers are encapsulated in a molding compound such as a plastics material to form a packaged device, leaving only the outer frame and undersides of the external connector pads exposed. The semiconductor die package is then cut (singulated) from the outer frame.
Semiconductor die packages are often assembled with an increased functionality and thus the number of external connectors (pin count) must often be increased to accommodate the increased functionality and power supply rail requirements of the semiconductor die. The number of external connectors is due to the increase in the number of die connection pads comprising power rail pads, ground rail pads and data input and output pads. However, the number of lead fingers is limited by the size of the package and lead finger pitch.
Lengths of the lead fingers may extend outside the mold compound, or in the case of surface mounted semiconductor packages, a surface of the lead fingers is exposed at the bottom of the package for electrical connection to a circuit board. An example of a surface mounted package is the Quad Flat Non-leaded (QFN) package, which includes exposed contact pads or terminals beneath and on four sides of a rectangular semiconductor package. It would therefore be advantageous if semiconductor packages could have both lead fingers extending outside peripheral edges of the packaging compound (package housing) and lead fingers allowing for surface mounting whilst maintaining a relatively small footprint.